Structural alterations of airway epithelial tight junctions in cystic fibrosis: comparison of transplant and postmortem tissue

Claudin-1 as a novel target gene induced in obesity and associated to inflammation, fibrosis, and cell differentiation

OBJECTIVE

T lymphocytes from visceral and subcutaneous white adipose tissues (vWAT and sWAT, respectively) can have opposing roles in the systemic metabolic changes associated with obesity. However, few studies have focused on this subject. Claudin-1 (CLDN1) is a protein involved canonically in tight junctions and tissue paracellular permeability. We evaluated T-lymphocyte gene expression in vWAT and sWAT and in the whole adipose depots in human samples.

METHODS

A Clariom D-based transcriptomic analysis was performed on T lymphocytes magnetically separated from vWAT and sWAT from patients with obesity (Cohort 1; N = 11). Expression of candidate genes resulting from that analysis was determined in whole WAT from individuals with and without obesity (Cohort 2; patients with obesity: N = 13; patients without obesity: N = 14).

RESULTS

We observed transcriptional differences between T lymphocytes from sWAT compared with vWAT. Specifically, CLDN1 expression was found to be dramatically induced in vWAT T cells relative to those isolated from sWAT in patients with obesity. CLDN1 was also induced in obesity in vWAT and its expression correlates with genes involved in inflammation, fibrosis, and adipogenesis.

CONCLUSION

These results suggest that CLDN1 is a novel marker induced in obesity and differentially expressed in T lymphocytes infiltrated in human vWAT as compared with sWAT. This protein may have a crucial role in the crosstalk between T lymphocytes and other adipose tissue cells and may contribute to inflammation, fibrosis, and alter homeostasis and promote metabolic disease in obesity.

The PDZ motif peptide of ZO-1 attenuates Pseudomonas aeruginosa LPS-induced airway inflammation

Pseudomonas aeruginosa is known to play a role in many human diseases. Therefore, examining the negative control mechanisms of tight junction protein ZO-1 on the exotoxin LPS of P. aeruginosa-induced diseases could be critical in the development of novel therapeutics. We found that ZO-1 expression dramatically decreased in inflammatory human lung tissues. Interestingly, PDZ1 deletion of the PDZ domain in the ZO-1 protein dramatically decreased LPS-induced F-actin formation and increased the expression of genes for pro-inflammatory cytokines, but not PDZ2 and PDZ3 of the ZO-1 protein. We also found that the consensus PDZ peptide (based on PDZ1) of ZO-1 down-regulates the expression of pro-inflammatory cytokine genes and F-actin formation; in contrast, the GG24,25AA mutant PDZ peptide cannot control these genes. LPS activates IL-8 secretion extracellularly in a time-dependent manner, while the secretion is inhibited by PDZ peptide. Whereas increased IL-8 secretion by LPS activates the CXCR2 receptor, overexpressed RGS12 negatively regulates LPS-induced CXCR2/IL-8 signaling. The PDZ peptide also decreases LPS-induced inflammatory cell populations, pro-inflammatory cytokine gene expression, and TEER in bronchoalveolar lavage fluid and cultured alveolar macrophages. Collectively, we suggest that the PDZ peptide may be a potential therapeutic for bacteria-induced respiratory diseases.

Invited review: human air-liquid-interface organotypic airway tissue models derived from primary tracheobronchial epithelial cells-overview and perspectives

The lung is an organ that is directly exposed to the external environment. Given the large surface area and extensive ventilation of the lung, it is prone to exposure to airborne substances, such as pathogens, allergens, chemicals, and particulate matter. Highly elaborate and effective mechanisms have evolved to protect and maintain homeostasis in the lung. Despite these sophisticated defense mechanisms, the respiratory system remains highly susceptible to environmental challenges. Because of the impact of respiratory exposure on human health and disease, there has been considerable interest in developing reliable and predictive in vitro model systems for respiratory toxicology and basic research. Human air-liquid-interface (ALI) organotypic airway tissue models derived from primary tracheobronchial epithelial cells have in vivo–like structure and functions when they are fully differentiated. The presence of the air-facing surface allows conducting in vitro exposures that mimic human respiratory exposures. Exposures can be conducted using particulates, aerosols, gases, vapors generated from volatile and semi-volatile substances, and respiratory pathogens. Toxicity data have been generated using nanomaterials, cigarette smoke, e-cigarette vapors, environmental airborne chemicals, drugs given by inhalation, and respiratory viruses and bacteria. Although toxicity evaluations using human airway ALI models require further standardization and validation, this approach shows promise in supplementing or replacing in vivo animal models for conducting research on respiratory toxicants and pathogens.

Vitamin D supplementation of initially vitamin D-deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB/c dams were fed a vitamin D₃‐supplemented (2280 IU/kg, VitD⁺) or nonsupplemented (0 IU/kg, VitD⁻) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD⁻ diet were switched to a VitD⁺ diet from 8 weeks of age (VitD^−/+). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid (BALF) of VitD⁻ mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D₃. There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD⁺ mice compared to VitD⁻ mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D₃‐containing diet (VitD^−/+). Reduced total IgM levels were detected in BALF and serum of VitD^−/+ mice compared to VitD⁺ mice. Lung mRNA levels of the vitamin D receptor (VDR) were greatest in VitD^−/+ mice. Total IgG levels in BALF were greater in mice fed the vitamin D₃‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D₃ suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.

Airway Epithelium Dysfunction in Cystic Fibrosis and COPD

Cystic fibrosis is a genetic disease caused by mutations in the CFTR gene, whereas chronic obstructive pulmonary disease (COPD) is mainly caused by environmental factors (mostly cigarette smoking) on a genetically susceptible background. Although the etiology and pathogenesis of these diseases are different, both are associated with progressive airflow obstruction, airway neutrophilic inflammation, and recurrent exacerbations, suggesting common mechanisms. The airway epithelium plays a crucial role in maintaining normal airway functions. Major molecular and morphologic changes occur in the airway epithelium in both CF and COPD, and growing evidence suggests that airway epithelial dysfunction is involved in disease initiation and progression in both diseases. Structural and functional abnormalities in both airway and alveolar epithelium have a relevant impact on alteration of host defences, immune/inflammatory response, and the repair process leading to progressive lung damage and impaired lung function. In this review, we address the evidence for a critical role of dysfunctional airway epithelial cells in chronic airway inflammation and remodelling in CF and COPD, highlighting the common mechanisms involved in the epithelial dysfunction as well as the similarities and differences of the two diseases.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

Molecular aspects of tight junction barrier function

In complex multicellular organisms, epithelia lining body cavities regulate absorption and secretion of ions, organic molecules, and water. Proper function of epithelia depends on apically and basolaterally situated ion channels as well as tight junctions which seal the apical intercellular space. Without tight junctions, transepithelial concentration gradients of ions and nutrients would be dissipated through the paracellular space. Elevated tight junction permeability is a feature of many diseases of multiple organs, including the gastrointestinal tract [1,2,3(•),4(•)], kidney [5,6], and lungs [7,8]. In the intestines, epithelial barrier dysfunction is a major contributor to diarrhea and malnutrition and is associated with significant morbidity and mortality worldwide.

Breaking barriers. New insights into airway epithelial barrier function in health and disease

Epithelial permeability is a hallmark of mucosal inflammation, but the molecular mechanisms involved remain poorly understood. A key component of the epithelial barrier is the apical junctional complex that forms between neighboring cells. Apical junctional complexes are made of tight junctions and adherens junctions and link to the cellular cytoskeleton via numerous adaptor proteins. Although the existence of tight and adherens junctions between epithelial cells has long been recognized, in recent years there have been significant advances in our understanding of the molecular regulation of junctional complex assembly and disassembly. Here we review the current thinking about the structure and function of the apical junctional complex in airway epithelial cells, emphasizing the translational aspects of relevance to cystic fibrosis and asthma. Most work to date has been conducted using cell culture models, but technical advancements in imaging techniques suggest that we are on the verge of important new breakthroughs in this area in physiological models of airway diseases.

Lung endothelial cells strengthen, but brain endothelial cells weaken barrier properties of a human alveolar epithelium cell culture model

The blood-air barrier in the lung consists of the alveolar epithelium, the underlying capillary endothelium, their basement membranes and the interstitial space between the cell layers. Little is known about the interactions between the alveolar and the blood compartment. The aim of the present study was to gain first insights into the possible interplay between these two neighbored cell layers. We established an in vitro Transwell model of the alveolar epithelium based on human cell line H441 and investigated the influence of conditioned medium obtained from human lung endothelial cell line HPMEC-ST1.6R on the barrier properties of the H441 layers. As control for tissue specificity H441 layers were exposed to conditioned medium from human brain endothelial cell line hCMEC/D3. Addition of dexamethasone was necessary to obtain stable H441 cell layers. Moreover, dexamethasone increased expression of cell type I markers (caveolin-1, RAGE) and cell type II marker SP-B, whereas decreased the transepithelial electrical resistance (TEER) in a concentration dependent manner. Soluble factors obtained from the lung endothelial cell line increased the barrier significantly proven by TEER values and fluorescein permeability on the functional level and by the differential expression of tight junctional proteins on the molecular level. In contrast to this, soluble factors derived from brain endothelial cells weakened the barrier significantly. In conclusion, soluble factors from lung endothelial cells can strengthen the alveolar epithelium barrier in vitro, which suggests communication between endothelial and epithelial cells regulating the integrity of the blood-air barrier.

Heregulin activation of ErbB2/ErbB3 signaling potentiates the integrity of airway epithelial barrier

BACKGROUND

Members of the ErbB family of the receptor protein tyrosine kinase superfamily mediate heregulin (HRG)-induced cell responses. Here we investigated HRG activation of ErbB receptors, and the role of this activation in the development of the permeability barrier in airway epithelial cells (AECs).

METHODS

Two airway epithelial-like cell lines, Calu-3 and 16HBE were exposed to HRG or no stimulus and were evaluated with respect to their paracellular permeability as determined by transepithelial electric resistance (TER) and fluorescein isothiocyanate (FITC)-dextran flux. Tight junctions (TJs) were assessed by immunocytochemical localization of occludin and zonula occludens-1.

RESULTS

HRG promoted the development of the permeability barrier and TJ formation by monolayers of Calu-3 and 16HBE cells. Calu-3 cells expressed ErbB1, ErbB2, and ErbB3, but not ErbB4, on their surface. ErbB3 knockdown by small interference RNA (siRNA) blunted the effects of HRG on the permeability barrier. ErbB3 is known as a kinase-dead receptor and relies on other members of the family for its phosphorylation. To identify its heterodimerization partner, we knocked down the expression of other ErbB family receptors. We found that HRG's effect on the permeability barrier could be significantly attenuated by transfecting cells with ErbB2 siRNA but not with EGFR siRNA.

CONCLUSION

These results indicate that HRG activation of ErbB2/ErbB3 heterodimers is essential for regulation of the permeability barrier in AECs.

LXA4 stimulates ZO-1 expression and transepithelial electrical resistance in human airway epithelial (16HBE14o-) cells

Lipoxin A(4) (LXA(4)) is a biologically active eicosanoid produced in human airways that displays anti-inflammatory properties. In cystic fibrosis and severe asthma, LXA(4) production has been reported to be decreased, and, in such diseases, one of the consequences of airway inflammation is disruption of the tight junctions. In the present study, we investigated the possible role of LXA(4) on tight junction formation, using transepithelial electrical resistance (TER) measurements, Western blotting, and immunofluorescence. We observed that exposure to LXA(4) (100 nM) for 2 days significantly increased zonula occludens-1 (ZO-1), claudin-1, and occludin expression at the plasma membrane of confluent human bronchial epithelial 16HBE14o- cells. LXA(4) (100 nM) stimulated the daily increase of the 16HBE14o- cell monolayer TER, and this effect was inhibited by boc-2 (LXA(4) receptor antagonist). LXA(4) also had a rapid effect on ZO-1 immunofluorescence at the plasma membrane and increased TER within 10 min. In conclusion, our experiments provide evidence that LXA(4) plays certainly a new role for the regulation of tight junction formation and stimulation of the localization and expression of ZO-1 at the plasma membrane through a mechanism involving the LXA(4) receptor.

Role of claudin interactions in airway tight junctional permeability

Airway epithelial tight junctions (TJs) serve to separate the external and internal environments of the lung. However, the members of the claudin family that mediate this function have not been fully delineated. We characterized the claudin expression in normal airways removed from human donors during lung transplantation and determined the contribution of each claudin to airway barrier function. Stable cell lines in NIH/3T3 and human airway (IB3.1) cells were constructed expressing the claudin components found in the human airway, claudin-1, -3, or -5. The effects of claudin expression on transepithelial resistance, permeability coefficients, and claudin-claudin interactions were assessed. Claudin-1 and -3 decreased solute permeability, whereas claudin-5 increased permeability. We also detected oligomerization of claudin-5 in cell lines and in freshly excised human airways. Coimmunoprecipitation studies revealed heterophilic interactions between claudin species in both cell lines and human airway epithelium. These suggest that airway TJs are regulated by claudinclaudin interactions that confer the selectivity of the junction.

EGTA enhancement of adenovirus-mediated gene transfer to mouse tracheal epithelium in vivo

Administration of recombinant adenoviral (AdV) vectors to animals can lead to inflammatory and immune responses. For therapeutic indications in which repeated treatment is necessary, such as cystic fibrosis (CF), these responses can limit the therapeutic usefulness of the vector. In principle, the utility of the vector can be improved by increasing its therapeutic index, that is, by either increasing its efficacy or decreasing its toxicity. A strategy that would enhance the efficacy of an adenoviral approach would allow the use of fewer virus particles to achieve a given level of transgene expression, and thereby also reduce unwanted effects such as immune responses. Following up on our observation that treating polarized normal human bronchial epithelial cells with calcium (Ca(2+))-free medium or the calcium chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) significantly enhanced the subsequent transfection of these cells with cationic lipid:pDNA complexes, we have now asked whether such a treatment protocol might also improve the ability of AdV to infect these cells. Treating polarized airway epithelial cells with EGTA led to a dramatic increase in AdV-mediated transduction, as demonstrated by an approximately 50-fold increase in transgene expression. This strategy was also tested in vivo and resulted in substantial increases (up to 50-fold) in the ability of AdV vectors to infect mouse tracheal epithelium. Transfection of mouse trachea with an AdV aerosol was also significantly increased by pretreatment with EGTA. The enhancing effects of EGTA could not be duplicated with hypo- or hyperosmotic treatments. Light microscopy of mouse trachea that had been EGTA treated and then infected with AdV demonstrated an EGTA-mediated AdV infection of airway epithelial cells. The apparent enhanced potency of AdV for airway cells resulting from this strategy provides a significant increase in the therapeutic index of this gene delivery vector, and may increase the likelihood that it can be used for clinical indications requiring chronic administration of the vector.

Regulation of the intestinal epithelial paracellular barrier

Paracellular transport of orally-administered drugs, the passage of molecules between adjacent intestinal epithelial cells, is impeded by a range of structural and functional features found in the intestine. An increased knowledge of the mechanisms that govern the paracellular barrier will enable the pharmaceutical scientist to design novel and rational formulations and delivery platforms that will improve the oral bioavailability of therapeutic molecules, particularly proteins and peptides, which would be taken-up by the paracellular pathway.

Human airway epithelial tight junctions

The flux of fluid, ions, macromolecules, and inflammatory cells across airway epithelium depends in part upon the integrity of its apico-lateral tight junctions. Without the correct balance of fluid and ions, the normal functioning of mucociliary clearance and the neural responsiveness of the airways cannot take place. Freeze-fracture electron microscopy has been used to investigate the structure of human airway tight junctions and their morphology comprehensively characterised at two airway levels (main and lobar bronchi). Further data is needed to establish if the fall in transepithelial electrical resistance found across progressively proximal disparate airway generations is correlated with an alteration in tight junction morphology. Altered epithelial permeability is associated with the development of the airway conditions: asthma, chronic bronchitis, and cystic fibrosis. However, few data have been published on the structure of tight junctions in asthma and chronic bronchitis. In patients with cystic fibrosis, airways obtained at transplantation and postmortem show a basal extension of the apico lateral tight junctional belt. This change is not unique to cystic fibrosis airways as it also occurs in non-respiratory systems postmortem. However the functional relevance of these changes remains uninvestigated and recently developed in vitro models may help answer this question. The data demonstrate that tight junctions are highly dynamic structures capable of rapid alterations in disease and in response to functional stress.

Proteinase-free myeloperoxidase increases airway epithelial permeability in a whole trachea model

In cystic fibrosis the bronchiectatic conducting airways have large numbers of neutrophils in their walls and in their luminal contents. The neutrophil's primary granule enzyme activities of elastase and peroxidase are increased in the sputum of these patients. It has been postulated that these enzymes--together or individually--act to damage the airway epithelium. However, only peroxidase activity has consistently correlated with the degree of structural and functional airway disease in these patients with leakage of plasma protein into the airway lumen (Regelmann et al., Pediatr Pulmonol, 1995; 19:1-9). The present study was designed to test whether human neutrophil-derived myeloperoxidase can independently produce bronchial epithelial damage without the presence of proteases, as measured by increased permeability of the airway epithelium. Human peripheral blood neutrophils were purified, their primary granules isolated, and their peroxidase purified using affinity and ion exchange column chromatography. Activity of the proteinase-free peroxidase was measured using a chromogenic substrate. The effect of this peroxidase on the permeability of excised rat tracheas was measured using radioactive and fluorescent-labeled non-ionic molecules of varying molecular weight. Rat tracheas exposed to 15 minute treatments with either 130 U of peroxidase or hydrogen peroxide (10(-5) M) did not show a significant increase in the permeability of the epithelium to [3H]inulin, [14C]sucrose, and fluorescein isothiocyanate dextran 20 compared with control tracheas. However, those tracheas exposed to 130 U peroxidase followed by 10(-5) M hydrogen peroxide showed an increased permeability to each of the three test solutes. We conclude that proteinase-free myeloperoxidase, in the presence of non-toxic concentrations of its substrates, hydrogen peroxide and halide, produced increases in permeability to non-ionic molecules in the rat trachea within 15 minutes.